The present application generally relates to an improved viscosity modifier. In particular, the present application relates to microfibrous cellulose (MFC) having improved performance.
Viscosity modifiers are used in a variety of products—from foods, pharmaceuticals, and cosmetics to oil field drilling fluids. One such viscosity modifier is microfibrous cellulose (MFC), also known as reticulated cellulose or as microfibrillated cellulose, which may be produced by fermentation of Acetobacter xylinum. This bacteria produces cellulose that is chemically identical to plant-derived cellulose. Although identical in chemical structure, bacterial-produced MFC fibers may be smaller in diameter than plant-derived cellulose fibers, thereby giving the MFC a greater surface area. This high surface area allows MFC to create three-dimensional networks that produce a desirable yield value in solution at low use levels.
MFC is essentially insoluble and uncharged and, therefore, may not be not adversely affected by ionic environments. Because MFC is essentially insoluble, it does not compete for water and, therefore, has a wide range of compatibility and is much less susceptible to degradation than water-soluble polysaccharides. For example, MFC is compatible with both concentrated anionic aqueous solutions, such as heavy brines used in oilfield applications, and in high surfactants systems, such as liquid dish and laundry detergents (see, e.g., U.S. Published Patent Application Nos. 2008/0108541 and 2008/0108714). MFC also is compatible with cationic systems, such as fabric softeners using cationic softening agents and anti-microbial cleaners that use benzylalkonium chlorides (see, e.g., U.S. Pat. No. 6,241,812 and U.S. Pat. No. 7,888,308). MFC also can be used in polyol systems (see, e.g., U.S. Pat. No. 5,951,910) such as in essentially pure glycerin, ethylene glycol, propylene glycol, and polyethylene glycol systems.
MFC has been produced commercially in several different forms. For example, CP Kelco produced a commercial MFC in the form of a wet cake (resembling wet cardboard) for several years that was later discontinued. This form of MFC was typically about 10-20 wt % solids and the balance water. A small amount of sorbic acid preservative was added to prevent mold. This form of MFC was processed using multiple rinse cycles, which led to significant product loss in recovery, and also included strong alkali treatment, which appears to have led to a decrease in MFC efficiency.
Dry powder forms of MFC also are commercially available, including both discontinued products (e.g., PrimaCel™) and presently available products (e.g., AxCel® PX, AxCel® CG-PX, Axcel® PG, Cellulon® PX, and various “K”-named products available from CP Kelco, Atlanta, Ga.). Dry powder forms were created to improve handling and logistics for delivery to customers (e.g., issues and costs associated with transporting water). These commercial versions of powdered MFC can be used to provide suspension in many applications, such as surfactant-thickened and high surfactant systems (see, e.g., U.S. Published Patent Application Nos. 2008/0108541 and 2008/0108714, and U.S. Pat. No. 7,888,308, the disclosures of which are herein incorporated by reference for their relevant teachings on MFC and MFC/surfactant systems). These commercial versions of powdered MFC generally include blends of MFC and various co-agents, such as, but not limited to, carboxymethyl cellulose (CMC), xanthan gum, guar, pectin, gellan, carrageenan, locust bean gum, gum Arabic, cationic guar, cationic hydroxyethyl cellulose (HEC), and the like. Additional information regarding MFC systems can be found, for example, in U.S. Published Patent Application No. 2007/0027108 and U.S. Pat. No. 8,053,216, the disclosures of which are incorporated herein by reference for their relevant teachings on MFC and MFC systems with co-agents.
These co-agents allow the drying and milling of MFC into a powdered product. Without these co-agents, MFC can lose a high degree of its functionality after drying and milling due to an irreversible agglomeration of the MFC during the drying process known as hornification. Blends of MFC with co-agents, however, may limit how the powdered MFC can be used in products due to compatibility limitations of the co-agents. For example, while MFC is uncharged, most of the co-agents that are used are either anionic or cationic. Thus, commercial MFC powdered products containing anionic co-agents, such as CMC or xanthan gum, may have compatibility issues when used in products with, for instance, cationic surfactants. Additionally, commercial MFC powdered products may have limited compatibility with products that contain high levels of water-miscible organic solvents, such as glycols or glycerol. When used with such organic solvents, the co-agents from the commercial MFC may form precipitates which may result in poor clarity and poor yield values (i.e., poor suspension properties). Finally, the use of activated solutions (i.e., highly dispersed solutions of MFC prepared by using high shear mixing such as high speed rotor stator devices or high pressure homogenization devices) of powdered MFC may restrict the order in which other ingredients are added to a product formulation, so as to prevent issues such as co-agents forming precipitates.
In addition, it has recently been discovered that irreversible losses in the MFC performance may result from manufacturing of the wet-cake and dry powdered forms of the MFC. For example, the wet-cake MFC was purified by lysing the bacteria cells during a highly caustic, hot-digestion step which was believed to be necessary to solubilize the cellular debris for subsequent removal during washing steps in the process. The processing of the wet-cake MFC began immediately after fermentation with a concentration step using a belt press. The concentrated MFC was then re-slurried with soft water to a concentration of around 2% by weight MFC, and the pH was raised to about 13. The MFC slurry was then held at pH 13 for about 3 hours at 150° F. Following the caustic digestion, the material was again concentrated and re-slurried in soft water up to 4 times. These treatments appear to have led to significant losses of MFC fiber and resulted in reduced performance.
Accordingly, there exists a need to provide a form of MFC product for use in a wide variety of product formulations that increases the efficiency of the MFC over current commercially available forms of MFC.